Surface acoustic waves have become an important and useful technology, with applications that include spread spectrum communications. Beam compression is useful to increase the effective energy density of the beam. This has been accomplished by several methods: parabolic horn compressors, track changing multistrip couplers, and reflecting array compressors. Each of these beam compression techniques, however, has an inherent distortion in the way the signal is processed. The parabolic horn has dispersion at the reflecting surfaces, additional losses multimoding and additional length. For example, see "Broadband, Amplitude and Phase Compensating Transducers for Monolithic Convolvers", W. R. Smith, 1980 Ultrasonics Symposium, IEEE Transactions on Sonics and Ultrasonics.
Track changing multistrip couplers and reflecting array compressors both have a problem with an asymmetric side lobe which is difficult to remove. See "Improvements in Metalized R.A.C. Design", J. T. Godfrey, et al, July 4, 1978 Ultrasonics Symposium, IEEE Transactions on Sonics and Ultrasonics. See also C. Maerfeld, Wave Electronics, Vol. 2, (1976), p. 105, Elsevier Scientific Publishing Co., Amsterdam.
Accordingly, the objective of the present invention is to reduce distortion of the wave undergoing compression and to increase the efficiency of the compressor.